FIG. 4 shows a prior art liquid phase crystal growth apparatus for hetero-epitaxial liquid phase growth. In FIG. 4, reference numeral 1 designates a melt boat and a lid 2 is provided on the melt boat 1 to enclose the boat 1. Reference numeral 3 designates a first melt of a compound semiconductor contained in the first compartment of the boat 1 and reference numeral 4 designates a second melt of a compound semiconductor having a composition different from the first melt 3 contained in the second compartment of the boat 1. Reference numeral 6 designates a mother boat and reference numeral 5 designates a substrate placed in a concave part on the surface of the mother boat 6. Reference numeral 9 designates a quartz tube heated by a heater 10. Reference numerals 11a and 11b designate moving rods for moving the mother boat 6 and the melt boat 1, respectively.
FIGS. 5(a)-(d) show a prior art hetero-epitaxial liquid phase growth method.
FIG. 5(a) illustrates a temperature adjustment. The first melt 3 and the second melt 4 are airtightly enclosed by the melt boat 1 and the lid 2. The melts are positioned to one side of the substrate 5, which is placed on the mother boat 6, and are held in the melted state for a predetermined time.
Next, the entire boat, including the melt boat 1 and the mother boat 6, is cooled to lower its temperature at a predetermined speed, and when it reaches a predetermined temperature, the melt boat 1 is pushed by the moving rod 11b to the position shown in FIG. 5(b) such that the first melt 3 contacts the substrate 5. Then, a first epitaxial thin film is grown on the substrate 5.
Next, the melt boat 1 is pushed further by the moving rod 11b to the position shown in FIG. 5(c) such that the second melt 4 contacts the substrate 5 on which the first epitaxial thin film has been grown. Then, a second epitaxial thin film is grown on the first epitaxial thin film.
Finally, the melt boat 1 is pushed further by the moving rod 11b to the position shown in FIG. 5(d), and the substrate 5 is separated from the first and second melt 3 and 4, thereby completing the growth.
In this prior art example, the first thin film is epitaxially grown by using the first melt 3 and the second thin film is epitaxially grown by using the second melt 4.
In the prior art hetero-epitaxial liquid phase growth method, it is necessary to prepare a plurality of melts having different compositions for the hetero-epitaxial growth. Therefore, the melt production requires a lot of work and the materials are expensive.